This invention relates to a manufacturing method for a phenolic resol type resin foam having compact cellular structure, a high closed cell ratio and good heat resistance.
It is known that the cellular structure of phenolic resol type foams are affected by the type and mixing ratio of the phenol resins, the surface active agents, the blowing agent, the curing agents, and the like. Also the foaming conditions such as a temperature etc., and above all, the type and mixing amount of surface active agents used affect the structure of the foam. Hitherto, as methods to obtain resol foams having a high closed-cell ratio, there are known methods of using a siloxane-oxyalkylene copolymer as the surface active agent, Japanese Patent Publication No. 15874/1970. A method of using a adduct of p-nonylphenol with an alkylene oxide as the surface active agent is known, Japanese Laid-Open Patent Publication No. 159836/1984. A method of using the adduct of dialkylphenol with alkylene oxide as the surface active agent, Japanese Laid-Open Patent Publication No. 226033/1984, is disclosed. However, even with these methods, a resol foam having an enough high closed-cell ratio, enough compact cellular structure and enough good heat resistance has not yet been obtained.
The inventors have conducted studies on surface active agents which can provide resole foams substantially improved as compared with those of the above-mentioned methods and as a result, have completed the present invention. The object of the invention is to provide resol foams having compact cellular structure, a high closed-cell ratio, and improved heat resistance.